1. Field of the Invention
The present invention relates to a method and apparatus for acquiring transmitted-radiation image data, and more particularly to a transmitted-radiation image data acquiring method and apparatus that is applied to a cone-beam computed tomograph (CT) which emits conical radiation to a subject in different directions of projection, acquires transmitted-radiation image data for each direction of projection, and generates volume data of the subject, based on the transmitted-radiation image data.
2. Description of the Related Art
In the field of medical imaging, research for detecting three-dimensional radiation image information has been undertaken. For example, a helical CT and a cone-beam CT have been proposed (see xe2x80x9cCone-Beam CTxe2x80x94Present Status and Future Prospects,xe2x80x9d Image Information (M), pp. 122-127, January 1988 and Japanese Unexamined Patent Publication No. 9(1997)-253079).
In the cone-beam CT, a radiation source and an area sensor (two-dimensional solid radiation detector) are disposed with a subject therebetween. While the radiation source and the area sensor are being rotated relatively with respect to the subject, conical radiation is emitted from the radiation source to the subject. The radiation transmitted through the subject is detected by the area sensor, whereby the transmitted-radiation image data of the subject is obtained at a different rotational position, i.e., for each direction of projection. Based on the obtained transmitted-radiation image data of the subject, the volume data of the subject is acquired. Based on the volume data of the subject, a three-dimensional image or a fault image is displayed on an image display such into as a CRT display, or the three-dimensional image or the like is temporarily stored in a storage device. Here, the solid radiation detector means a detector with a semiconductor device, which detects radiation and converts it to an electrical signal, as an essential part.
In the above-mentioned conventional cone-beam CT, incidentally, the area of a three-dimensional image or a fault image that can be displayed is an area which is formed by the overlapping portions in all directions of projection which the area sensor detects, specifically an inscribed circle of a total-radiation emitted area which is formed by conical radiation in each direction of projection that the area sensor can detect. That is, an image area that can be displayed is determined by the emission angle of radiation and the detection area of the area sensor. If the image area is enlarged, it will become necessary to emit conical radiation to the subject at a wider angle and to detect more of the wide-angle radiation transmitted through the subject with the area sensor. In other words, there is a need to employ a large-area sensor and to emit enough wide-angle radiation to cover the entire surface of the wide-area sensor to the subject.
However, it is difficult to fabricate a large-area sensor having a large detection area. Even if the sensor could be fabricated, it will be expensive, resulting in an increase in the cost of the cone-beam CT. For this reason, in the conventional cone-beam CT, it is difficult to display the image of a large area.
The present invention has been made in view of the aforementioned circumstances. Accordingly, it is an object of the present invention to provide a data acquiring method and apparatus which is capable of obtaining a large area quantity of transmitted-radiation image data without using a large-area sensor. Another object of the present invention is to provide a data acquiring method and apparatus that is capable of improving picture quality degradation due to scattered lines.
The first method according to the present invention is a method of acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the conical radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the method comprising the steps of
employing a line sensor as the solid radiation detector; and
obtaining an entire detection area quantity of transmitted-radiation image data by detecting the conical radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area for each direction of projection.
In the first method according to the present invention, an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area for each direction of projection. Therefore, the detection area can be enlarged and it becomes possible to acquire a larger area quantity of transmitted-radiation image data without using a large-area sensor. If the present invention is applied to the cone-beam CT, it will become possible to display a three-dimensional image or a fault image of a larger area.
Here, the xe2x80x9centire detection areaxe2x80x9d means the entire range of a desired area to be obtained. For example, when it is assumed that an area sensor is used as the solid radiation detector, the xe2x80x9centire detection areaxe2x80x9d is equivalent to the entire detection area of the area sensor.
Detecting the radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area means that any method may be employed if detection is performed by moving the line sensor so that the sensor covers the entire detection area. For example, a single line sensor may be moved so that it covers the entire detection area. Alternatively, a plurality of line sensors may be moved so that each line sensor covers a predetermined range and movement of each line sensor may be added up in order to cover the entire detection area.
Note that in moving the line sensor, it is preferable to move the line sensor along a circular arc with respect to the radiation source. The same applies to the following description.
The second method according to the present invention is a method of acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the cone radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the method comprising the steps of
employing a plurality of line sensors as the solid radiation detector;
dividing an entire detection area for each direction of projection into a plurality of division areas;
disposing each line sensor in each division area so that each line sensor is movable within the division area; and
obtaining an entire detection area quantity of transmitted-radiation image data by detecting the conical radiation transmitted through the subject with each line sensor, while each line sensor is being moved within each division area.
In the second method according to the present invention, the entire detection area for each direction of projection is divided into a plurality of division areas. Each line sensor is disposed in each division area so that each line sensor is movable within the division area, and an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with each line sensor, while each line sensor is being moved within each division area. Therefore, as with the aforementioned first method and apparatus, it becomes possible to acquire a larger area quantity of transmitted-radiation image data, while the movable range of each line sensor is being reduced. In addition, it becomes possible to display a three-dimensional image or a fault image of a larger area.
The third method according to the present invention is a method of acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the conical radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the method comprising the steps of constituting the solid radiation detector by a plurality of line sensors arranged to cover an entire detection area; and
obtaining an entire detection area quantity of transmitted-radiation image data by detecting the cone radiation transmitted through the subject with each line sensor.
In the third method according to the present invention, a plurality of line sensors arranged to cover an entire detection area are used as a solid radiation detector, and an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with each line sensor. Therefore, as with the aforementioned first method and apparatus, it becomes possible to acquire a larger area quantity of transmitted-radiation image data without moving each line sensor. In addition, it becomes possible to display a three-dimensional image or a fault image of a larger area.
Here, the xe2x80x9centire detection areaxe2x80x9d means an entire detection area for each direction of projection.
In either of the above-mentioned methods, it is preferable that substantially the rectilinear propagation component of the radiation, emitted from said radiation source and transmitted through said subject, be only incident on the line sensor (e.g., it is preferable to perform slit photographing). In this way, the influence of lines scattered at the subject can be suppressed.
In either method mentioned above, it is desirable to perform detection during the dilation period or contraction period of the heart in synchronization with the heartbeats of the subject. As a result, data can be obtained when the subject is substantially stationary. As a result, the image will not be obscure.
The first apparatus according to the present invention is an apparatus for acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the conical radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the apparatus comprising the radiation source;
a line sensor employed as the solid radiation detector;
means for moving the line sensor within an entire detection area for each direction of projection; and
data acquiring means for acquiring an entire detection area quantity of transmitted-radiation image data by detecting the cone radiation transmitted through the subject with the line sensor at each moved position.
In the first apparatus according to the present invention, an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with the line sensor, while the line sensor is being moved within the entire detection area for each direction of projection. Therefore, the detection area can be enlarged and it becomes possible to acquire a larger area quantity of transmitted-radiation image data without using a large-area sensor. If the present invention is applied to the cone-beam CT, it will become possible to display a three-dimensional image or a fault image of a larger area.
The second apparatus according to the present invention is an apparatus for acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the conical radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the apparatus comprising the radiation source;
a plurality of line sensors employed as the solid radiation detector, each line sensor being disposed so that the line sensor is movable within each of a plurality of division areas formed by dividing an entire detection area;
means for moving each the line sensor within each division area for each direction of projection; and
data acquisition means for acquiring an entire detection area quantity of transmitted-radiation image data by detecting the conical radiation transmitted through the subject with each the line sensor at each moved position.
In the second apparatus according to the present invention, the entire detection area for each direction of projection is divided into a plurality of division areas. Each line sensor is disposed in each division area so that each line sensor is movable within the division area, and an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with each line sensor, while each line sensor is being moved within each division area. Therefore, as with the aforementioned first method and apparatus, it becomes possible to acquire a larger area quantity of transmitted-radiation image data, while the movable range of each line sensor is being reduced. In addition, it becomes possible to display a three-dimensional image or a fault image of a larger area.
The third apparatus according to the present invention is an apparatus for acquiring transmitted-radiation image data on a subject, by emitting conical radiation from a radiation source toward the subject and by detecting the conical radiation transmitted through the subject with a solid radiation detector, while the radiation source and the solid radiation detector disposed with the subject therebetween are being rotated relatively with respect to the subject;
the apparatus comprising the radiation source;
a plurality of line sensors employed as the solid radiation detector, the plurality of line sensors being disposed to cover an entire detection area; and
data acquisition means for acquiring an entire detection area quantity of transmitted-radiation image data by detecting the conical radiation transmitted through the subject with each the line sensor.
In the third apparatus according to the present invention, a plurality of line sensors arranged to cover an entire detection area are used as a solid radiation detector, and an entire detection area quantity of transmitted-radiation image data is obtained by detecting the conical radiation transmitted through the subject with each line sensor. Therefore, as with the aforementioned first method and apparatus, it becomes possible to acquire a larger area quantity of transmitted-radiation image data without moving each line sensor. In addition, it becomes possible to display a three-dimensional image or a fault image of a larger area.
In the aforementioned second and third data acquiring apparatuses, it is preferable that the line sensors be provided on a circular arc with respect to the radiation source. In this way, the distance between the radiation source and each line sensor can be made the same. Since no image distortion based on a difference in distance occurs, the correction of a magnification ratio becomes unnecessary.
In either apparatus mentioned above, it is also desirable to provide incident-direction control means, such as a slit and the like, which causes substantially the rectilinear propagation component of the radiation, emitted from the radiation source and transmitted through the subject, to be only incident on the line sensor. As a result, the influence of lines scattered at the subject can be suppressed.
In addition, it is desirable that the incident-direction control means be provided between the line sensors and the subject and between the radiation source and the subject. It is even desirable that the incident-direction control means be provided in circular arc form with respect to the radiation source.
Furthermore, it is desirable that either apparatus mentioned above be provided with synchronization means which performs detection during the dilation period or contraction period of the heart in synchronization with the heartbeats of the subject. In this way, data can be obtained when the subject is substantially stationary. As a result, the image will not be obscure.
In the aforementioned, the line sensor means a solid radiation detector with a narrow width and a long length. The line sensor is not limited to a one-dimensional solid sensor with a width equivalent to one pixel, but may be any sensor if it has a comparatively narrower width and a long length.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative example.